Gallium arsenide semiconductor technology has been evolving rather quickly in recent years. This rapid evolution stems from the fact that gallium arsenide is a semiconductor material which has high electron mobility which thus holds the promise of high-performance, ultra-high speed logic circuits. The development of silicon-integrated circuits has made available a vast art encompassing lithography, surface preparation, film deposition and design. One would like to be able to apply this new technology to GaAs semiconductors, but for reasons clearly due to the difference in the nature of these materials and their surfaces, new art must be developed to advance the fabrication of dense circuits on gallium arsenide. Considerable interface investigation has been directed toward the formation of high quality Schottky barrier interfaces and low resistance Ohmic contacts for interconnections on gallium arsenide. The Schottky barrier contact can be used to control charge in the interior of gallium arsenide devices and the Ohmic contact is used by the devices to communicate with the outside world. Some of the problems associated with forming reliable and device repeatable Schottky barrier interfaces and low resistance Ohmic contacts on gallium arsenide-based systems, as well as some of the attempts in the prior art to overcome these problems, are described in an article entitled "Contact and Metallization Problems in Gallium Arsenide Integrated Circuits" by N. Braslau in the Journal of Vacuum Science Technology A, volume four (4), number six (6), November/December 1986, pages 3085 to 3090. The author of that article points out that there is a distinct trend toward the use of refractory metal contacts due to the elevated temperatures to which they are subjected during processing which cause severe degradation to the presently used gold-based metallurgy. Thus for example, the prior art requires deposition of an alloy, typically gold germanium nickel followed by an annealing process at elevated temperature to initiate interdiffusion of the contact metal with the semiconductor, gallium arsenide. Unfortunately, this process requires precise control and the high temperatures which are incompatible with other processing requirements. The metallurgy of this contact technology has been extensively studied over the past twenty years and has been shown to be chemically complex and spatially heterogeneous. Thus, it would be highly desirable to provide a method for forming Ohmic contacts on gallium arsenide surfaces at temperatures sufficiently low to preclude deleterious effects on the semiconductor structure. It would also be highly desirable to utilize such a low temperature formation process to provide Schottky barrier contacts with a characteristic barrier height for gallium arsenide that is repeatable from device to device and which has an ideality factor approaching one, by providing a uniform diffusion barrier that exhibits relatively homogeneous, spatial uniformity over the contact surface area.
Information on existing methods for preparation of Schottky barriers using chemical etching techniques may be found, by way of example, in the text entitled "VLSI Fabrication Principals-Silicon and Gallium Arsenide" by Sorab K. Ghandhi published in 1983 by John Wiley & Sons, Inc. at pages 520 to 523.